Sunglasses have been used for many years as cosmetic devices and to reduce the intensity of visible light. More recently, they have come to be seen as important in protecting a wearer's eyes from exposure to harmful solar radiation, in particular, ultraviolet (UV) rays that can cause irreparable damage to the eye. Visible light ranges from about 700 nm to 380 nm, the region below about 380 nm being considered the ultraviolet region. Wavelengths from 290 to 315 nm, referred to as UVB, are potentially more damaging than those in the range of 315 to 380 nm, referred to as UVA. Excessive exposure of the eyes to ultraviolet rays can damage the cornea and lens of the eye, and longtime exposure to UV radiation contributes to some types of cataracts. The light sensitive retina at the back of the eye can also be injured because the lens shields it from UV rays.
The lenses of higher quality sunglasses contain UV absorbers to protect the wearer's eyes from these damaging rays. UV absorbers are often included in the glass or plastic material used to make the lenses. They have also been included in lens coatings and, in the case of polarized lenses discussed in more detail below, in polarizing film laminated into the lens structure.
Sunglasses are familiar devices generally constructed from a frame and one or more lenses. The lenses may be glass or plastic. These lens materials may contain light absorbing dyes and ultraviolet inhibiting chemicals and may have one or more coatings applied to the lens after it is formed.
While most sunglass lenses have a unitary construction using a single piece of lens material, some lenses are made from laminate materials. One type of laminate lens is a glass-plastic composite lens that combines the light weight of a plastic lens with the superior surface and optical qualities of glass. Examples of such composite lenses are found in U.S. Pat. Nos. 4,227,950, 5,323,191, and 5,364,487, the disclosures of which are incorporated herein by reference. These composites are usually formed by bonding preformed glass and plastic elements with an adhesive, although U.S. Pat. No. 4,227,950 teaches casting the plastic lens element against a preformed glass lens element. Also, U.S. Pat. No. 5,351,100 discloses a glass multifocal ophthalmic lens formed by fusing a glass multifocal lens portion to the convex outer surface of a second lens portion.
A distinct class of sunglass lens laminates comprises those incorporating polarizing films. Light waves from the sun are random non-polarized waves that, on reflection from a flat surface, become directional, or polarized. Glare is an example of light waves that have been restricted to one plane. Polarized sunglasses, which are effective at cutting surface reflection from flat surfaces such as water, ice, or roads, have lenses that typically include a polarizing layer laminated between two lens portions. Polarized sunglasses filter out glare, ultraviolet waves, and other random light by use of a polarized light filtering film commonly made of polyvinyl alcohol dyed with iodine. This film is constructed so that its crystal molecules are aligned in parallel lines. Light waves perpendicular to the plane of the crystals are blocked and light waves in the same plane as the crystals pass through the membrane, as described in U.S. Pat. No. 5,135,298.
Some adhesives used in lamination of lens portions have low concentrations of UV absorbers to prevent yellowing of the adhesive upon exposure to UV light, as described in U.S. Pat. No. 5,618,863, the disclosure of which is incorporated herein by reference.
There are many commercial examples of polarized lenses on the market. One type includes lenses that consist of two tempered clear glass lens portions. Another type includes lenses that consist of a tempered clear front glass and an untempered colored rear glass, with a mirror surface on the external convex surface and an antireflective coating on the external concave surface. Color may be added to the polarizing film and also incorporated into the rear lens. Another type of commercial lens has a clear and untempered front glass together with a clear and tempered rear glass, the mirror being on the front lens internal surface and the antireflective surface on the rear lens external surface. Color is in the polarizing film only. The laminates containing the polarizing film are usually prepared using an adhesive curable with ultraviolet light.
The manufacture of currently available polarizing lenses is a complex, time-consuming procedure with inconsistent results. Multiple lens portions must be kept in inventory and a high quantity of lenses failing quality tests leads to high costs. Furthermore, the polarization efficiency and the color transmission characteristics of the lens laminates may degrade unacceptably as a result of exposure to ultraviolet light during use.